Dictionary iteration in Python - Mini Project: Build & Apply

Dictionary iteration

📖 Scenario: You work in a small bookstore. You have a list of books with their prices stored in a dictionary. You want to check each book and its price to prepare a price list for customers.

🎯 Goal: Learn how to go through each item in a dictionary using a for loop and display the book names with their prices.

📋 What You'll Learn

Create a dictionary with book names as keys and prices as values

Create a variable to count how many books cost more than a certain price

Use a for loop with variables book and price to iterate over the dictionary items

Print the book names and prices in a readable format

Print the count of books that cost more than the given price

💡 Why This Matters

🌍 Real World

Bookstores and shops often keep product prices in dictionaries or similar data structures. Iterating over these helps prepare price lists or reports.

💼 Career

Knowing how to iterate over dictionaries is essential for data processing, reporting, and many programming tasks in software development and data analysis.

1

Create the books dictionary

Create a dictionary called books with these exact entries: 'Python Basics': 29.99, 'Data Science 101': 39.95, 'Machine Learning': 49.50, 'Deep Learning': 59.99, 'AI for Everyone': 24.99

Python

# Create the books dictionary with the given entries
# Your code here

Hint

Use curly braces {} to create a dictionary. Put book names as keys and prices as values separated by colons.

2

Set the price threshold

Create a variable called price_threshold and set it to 40. This will help us count books costing more than this price.

Python

books = {
    'Python Basics': 29.99,
    'Data Science 101': 39.95,
    'Machine Learning': 49.50,
    'Deep Learning': 59.99,
    'AI for Everyone': 24.99
}
# Create price_threshold variable and set it to 40
# Your code here

Hint

Just write price_threshold = 40 on a new line.

3

Count expensive books using a for loop

Create a variable called count_expensive and set it to 0. Then use a for loop with variables book and price to iterate over books.items(). Inside the loop, increase count_expensive by 1 if price is greater than price_threshold.

Python

books = {
    'Python Basics': 29.99,
    'Data Science 101': 39.95,
    'Machine Learning': 49.50,
    'Deep Learning': 59.99,
    'AI for Everyone': 24.99
}
price_threshold = 40
# Create count_expensive variable and set it to 0
# Use a for loop with book and price to iterate over books.items()
# Increase count_expensive by 1 if price > price_threshold
# Your code here

Hint

Start with count_expensive = 0. Then write for book, price in books.items():. Inside the loop, use an if to check price and add 1 to count_expensive.

4

Print the books and count

Use a for loop with variables book and price to iterate over books.items(). Inside the loop, print the book and price in this format: Book: {book}, Price: ${price} using an f-string. After the loop, print Number of books costing more than $40: {count_expensive}.

Python

books = {
    'Python Basics': 29.99,
    'Data Science 101': 39.95,
    'Machine Learning': 49.50,
    'Deep Learning': 59.99,
    'AI for Everyone': 24.99
}
price_threshold = 40
count_expensive = 0
for book, price in books.items():
    if price > price_threshold:
        count_expensive += 1
# Use a for loop to print each book and price in the format 'Book: {book}, Price: ${price}'
# Then print the count of expensive books
# Your code here

Hint

Use a for loop to print each book and price with print(f"Book: {book}, Price: ${price}"). Then print the count with print(f"Number of books costing more than $40: {count_expensive}").

Practice

1. What does the following code do?
for key in my_dict:

easy

A. Iterates over the keys of the dictionary

B. Iterates over the values of the dictionary

C. Iterates over the key-value pairs as tuples

D. Raises a syntax error

Solution

1. Step 1: Understand the for loop syntax

   The loop uses for key in my_dict, which by default iterates over dictionary keys.

2. Step 2: Identify what is accessed in each iteration

   Each iteration gives one key from the dictionary, not values or pairs.

3. Final Answer:

   Iterates over the keys of the dictionary -> Option A

4. Quick Check:

   for key in dict = keys [OK]

Hint: for key in dict loops over keys only [OK]

Common Mistakes:

• Thinking it loops over values
• Confusing keys with key-value pairs
• Assuming it raises an error

2. Which of the following is the correct syntax to iterate over keys and values in a dictionary my_dict?

easy

A. for key, value in my_dict.keys():

B. for key, value in my_dict:

C. for key in my_dict.values():

D. for key, value in my_dict.items():

Solution

1. Step 1: Recall dictionary methods for iteration

   To get keys and values, use my_dict.items() which returns key-value pairs.

2. Step 2: Check syntax correctness

   Only for key, value in my_dict.items(): correctly unpacks keys and values.

3. Final Answer:

   for key, value in my_dict.items(): -> Option D

4. Quick Check:

   Use dict.items() for keys and values [OK]

Hint: Use dict.items() to get keys and values together [OK]

Common Mistakes:

• Using my_dict without .items() for key-value pairs
• Trying to unpack keys() or values() which return single elements
• Syntax errors from missing .items()

3. What is the output of this code?

my_dict = {'a': 1, 'b': 2}
for k, v in my_dict.items():
    print(k, v)

medium

A. a 1\nb 2

B. ('a', 1)\n('b', 2)

C. a\nb

D. 1\n2

Solution

1. Step 1: Understand the loop over items()

   The loop unpacks each key-value pair from my_dict.items().

2. Step 2: Analyze the print statement

   It prints the key and value separated by space on each line, so output lines are "a 1" and "b 2".

3. Final Answer:

   a 1\nb 2 -> Option A

4. Quick Check:

   print(k, v) prints key and value separated by space [OK]

Hint: print(k, v) shows key and value separated by space [OK]

Common Mistakes:

• Expecting tuples printed instead of separate values
• Printing only keys or only values
• Confusing output format with list or tuple

4. Find the error in this code:

my_dict = {'x': 10, 'y': 20}
for key, value in my_dict:
    print(key, value)

medium

A. Dictionary keys cannot be unpacked

B. Incorrect print statement syntax

C. Missing .items() after my_dict

D. No error, code runs fine

Solution

1. Step 1: Identify the iteration target

   The loop tries to unpack two variables from my_dict directly, which yields only keys.

2. Step 2: Correct the iteration method

   To unpack key and value, use my_dict.items() instead of just my_dict.

3. Final Answer:

   Missing .items() after my_dict -> Option C

4. Quick Check:

   Use my_dict.items() to unpack key, value [OK]

Hint: Use .items() to unpack key and value in loop [OK]

Common Mistakes:

• Trying to unpack keys only without .items()
• Assuming dict directly yields key-value pairs
• Ignoring error message about unpacking

5. Given the dictionary data = {'a': 0, 'b': 2, 'c': 0, 'd': 4}, which code snippet creates a new dictionary with only keys having non-zero values?

hard

A. new_dict = {k: v for k, v in data if v != 0}

B. new_dict = {k: v for k, v in data.items() if v != 0}

C. new_dict = {k: v for k in data.keys() if data[k] != 0}

D. new_dict = {k: v for v, k in data.items() if v != 0}

Solution

1. Step 1: Understand dictionary comprehension with condition

   We want to keep only items where value is not zero, so use if v != 0 in comprehension.

2. Step 2: Check correct unpacking and syntax

   new_dict = {k: v for k, v in data.items() if v != 0} correctly unpacks key and value from data.items() and filters by value.

3. Final Answer:

   new_dict = {k: v for k, v in data.items() if v != 0} -> Option B

4. Quick Check:

   Use dict.items() and filter with if condition [OK]

Hint: Use dict.items() with if condition in comprehension [OK]

Common Mistakes:

• Forgetting .items() when unpacking key and value
• Swapping key and value in unpacking
• Using keys() without accessing values